test: add coverage for ParallelMap and ParallelFilter workers

Add tests to verify default worker behavior in ParallelMap and
ParallelFilter.
Add internal test to cover unexported Result marker methods for
coverage.

Makefile

@@ -6,7 +6,7 @@ build:
 	docker build -t $(IMAGE):latest .
 
 test: build
-	docker run --name $(IMAGE) --rm -i -t $(IMAGE) sh -c "$(TEST) $(COVER)"
+	docker run --name $(IMAGE) --rm -i $(IMAGE) sh -c "$(TEST) $(COVER)"
 
 scan:
 	trivy --cache-dir .trivycache/ image --exit-code 0  --no-progress --severity CRITICAL $(IMAGE)

parallel_filter_test.go

@@ -31,3 +31,12 @@ func TestParallelFilter_Error(t *testing.T) {
 	assert.Error(t, err)
 	assert.Nil(t, out)
 }
+
+func TestParallelFilter_DefaultWorkers(t *testing.T) {
+	values := []int{1, 2, 3, 4}
+	out, err := u.ParallelFilter(context.Background(), values, 0, func(_ context.Context, n int) (bool, error) {
+		return n%2 == 1, nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, []int{1, 3}, out)
+}

parallel_map_test.go

@@ -31,3 +31,12 @@ func TestParallelMap_Error(t *testing.T) {
 	assert.Error(t, err)
 	assert.Nil(t, out)
 }
+
+func TestParallelMap_DefaultWorkers(t *testing.T) {
+	values := []int{1, 2, 3}
+	out, err := u.ParallelMap(context.Background(), values, 0, func(_ context.Context, n int) (int, error) {
+		return n + 1, nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, []int{2, 3, 4}, out)
+}

result_internal_test.go

@@ -0,0 +1,12 @@
+package underscore
+
+import "testing"
+
+// Ensure the unexported marker methods are executed for coverage.
+func TestResultIsResultMarker(t *testing.T) {
+	var ok Ok[int]
+	ok.isResult()
+
+	var er Err[int]
+	er.isResult()
+}